A physical vapor deposition apparatus comprises a vacuum chamber having a target of a preselected material mounted thereon which is connected to a DC power supply; and a substrate which is mounted on a substrate support opposed to the target, which is connected to an RF power supply. During processing, the target material is bombarded with an inert gas, such as argon. Material from the target is dislodged or sputtered off and deposits onto the substrate, which can be for example a silicon wafer, a magnetic disk or a flat panel display. However, the sputtered material does not deposit in a line-of-sight direction only, and the sputtered material deposits on other parts of the chamber, such as the shield or clamping ring for the substrate.
In order to increase the directionality of the sputtered material onto the substrate, the use of a collimator has been suggested.
However, even when a collimator is used, the sputtered material deposits not only on the substrate, but also on surrounding parts of the chamber, such as clamping rings that hold the substrate onto the support during processing. Shields surrounding the substrate have been used to try to prevent sputtered material from depositing on the walls and other parts of the chamber. However, the shields become coated with the sputtered material and, due to build up of material that may have a coefficient of expansion different from that of the shield material itself, eventually results in flaking of the deposited material; this has the result that the deposited material forms particles in the chamber. Since deposition of these particles on the substrate may damage the small feature sized devices being made on the substrate, which would lower the yield of good devices, the formation of particles in the chamber must be avoided. Further, if there is any native oxide on the shield/clamping ring surfaces, the sputtered material does not adhere well and flaking results after fewer sputtering cycles than when the native oxide has been removed. Once flaking and particle generation has begun, the chamber must be disassembled and the various parts cleaned or replaced.
Thus it is also known to etch clean the shield and clamping ring periodically to remove native oxide and sputtered material. Removal of the native oxide improves the adhesion of sputtered material to the shield, thereby decreasing the likelihood that material will flake off to form particles, or at the least extends the number of sputtering cycles that can be run between cleanings or replacement of these parts. This etch cleaning process is described for example in U.S. Pat. No. 5,202,008 to Talieh et al, incorporated herein by reference. After reassembly of the chamber, parts will have formed a native oxide coating thereon, which also must be removed as explained above.
However, when a collimator is used in a physical vapor deposition (hereinafter PVD) chamber, such as is disclosed in U.S. Pat. No. 5,171,412 to Talieh et al, also incorporated hereby by reference, I have found that finely divided particles coat the bottom of the collimator facing the substrate. These particles can fall onto the surface of the substrate being coated, and thus their formation must be prevented.
Thus a method of in situ, periodic cleaning of a PVD chamber containing a collimator has been sought.